and to junebugblue, sorry about the other thread comment -- it was another member who had asked that question.
Gee --
If you are developing a highly interactive site with many different inputs and such... popups can be an extremely useful tool to use.
example:
User is entering information and choosing info from a dropdown box, but their choice isn't there.
Click a button to add a new entry. <click> Popup appears... they make a new entry, and click the close button. Once that happens, the parent page refreshes and their new entry appears in the dropdown box.
This is a great way to enforce business rules by giving users a very rigid data entry method, but offering them the functionality of adding new entries to the database. All the while, you are preserving the parent page so that they don't feel like they've gone anywhere else. Keeps the focus -- preserves look and feel, etc...
Just some random thoughts, because I used to be a very hard-core anti-popup person, too... until I realized some useful areas for them. Random ad popups are definitely the worst, though. ;-)